Method and apparatus for rolling strip

Abstract

A method of rolling strip in a strip rolling train having at least two roll stands, each roll stand having horizontally adjustable upper and lower work rolls, wherein the work rolls act alone as a two-high stand or each work roll is supported directly or through an intermediate roll by a back-up roll, or in a reversing stand in which at least two passes are rolled, wherein the strip is subjected in the roll stands to a constitutional change, and wherein adjusting elements act on the strip for imparting a profile and surface evenness to the strip. The method includes presupposing in at least one strip area an intended surface unevenness shape over a width of the strip, determining an actually achieved surface unevenness shape in the strip area and comparing the actually achieved surface unevenness shape to the presupposed unevenness shape, computing a difference between the unevenness shapes, and operating the adjusting elements such that the difference is minimized.

I claim: 
     
       1. A method of hot rolling strip in a hot strip rolling train having at least two roll stands, each roll stand having horizontally adjustable upper and lower work rolls, wherein the work rolls act alone as a two-high stand or each work roll is supported directly or through an intermediate roll by a back-up roll, or in a reversing stand in which at least two passes are rolled, wherein the hot strip is subjected in the roll stands to a constitutional change, and wherein adjusting elements act on the strip for imparting a profile and surface evenness to the strip, the method comprising presupposing in at least one strip area an intended surface unevenness shape over a width of the strip, determining an actually achieved surface unevenness shape in the strip area and comparing the actually achieved surface unevenness shape to the presupposed unevenness shape, computing a difference between the unevenness shapes, and operating the adjusting elements such that the difference is minimized, the intended hot strip unevenness leading, after cooling of the strip, to a desired cold strip evenness. 
     
     
       2. The method according to claim 1, comprising, in addition to presupposing an intended surface unevenness shape, presupposing a profile of intended tension distributions or intended elongations of the strip over the width thereof, comparing the intended tension distributions or intended elongations with actually achieved tension distributions or elongations, computing differences between the tension distributions and the elongations and utilizing the adjusting elements such that the differences are minimized. 
     
     
       3. The method according to claim 1, comprising, for producing a planar strip in a cold state, presupposing in the hot strip different surface unevenness shapes over the length of the strap. 
     
     
       4. The method according to claim 1, comprising, when a result of the minimization of the difference is insufficient, changing input conditions in the form of properties of the entering strip including strip contour, surface evenness shape and strip temperature distribution of the respective stand, and optimizing the result. 
     
     
       5. The method according to claim 1, comprising, for producing different strip surface unevenness shapes, adjusting work roll bending, PC stand adjusting angle, CVC displacement or additional mechanically or physically acting adjusting elements over the strip length so as to be constant or changeable. 
     
     
       6. The method according to claim 1, comprising carrying out description of intended values, surface unevenness shapes and mathematical evaluation by dividing the strip width into a body portion and an edge portion. 
     
     
       7. The method according to claim 1, comprising describing the surface unevenness shape by a polynom function y*=A 2  x 2  +A 4  x 4  +A 6  x 6  +A n  x n , wherein y* is a coordinate for strip elongation, strip surface unevenness or strip tension and x is a strip width coordinate. 
     
     
       8. The method according to claim 1, comprising alternatively describing the surface unevenness shape as a sequence of points. 
     
     
       9. The method according to claim 1, comprising describing the intended value for the surface unevenness shape by a polynom function y*=A 2  x 2  +A 4  x 4  +A 6  x 6  +A n  x n , or a sequence of points. 
     
     
       10. The method according to claim 1, comprising defining around intended values positive and negative limits of strip tension, surface evenness, strip elongation, strip shortening, and utilizing the adjusting elements such that strip tension distribution, surface evenness distribution, strip elongation distribution, strip shortening distribution are within the limits or exceeding of the limits is minimized. 
     
     
       11. The method according to claim 10, comprising describing the limits for a permissible surface unevenness shape by a polynom function y*=A 2  x 2  +A 4  x 4  +A 6  x 6  +A n  x n , or as a sequence of points. 
     
     
       12. The method according to claim 10, comprising providing different shapes and levels for the intended surface unevenness shapes and the evenness limits over the width of a strip for different stands or passes. 
     
     
       13. The method according to claim 10, comprising utilizing adjusting elements which influence the elastic behavior of the rolls for producing a strip elongation or strip shortening of a parabolic type or of a higher degree over the strip width, wherein the adjusting elements comprise one or both of axial displacement means for the work rolls or bending devices for the work rolls. 
     
     
       14. The method according to claim 1, comprising, for avoiding earing of the hot strip or in the cold state of the strip, carrying out a distribution of rolling forces such that the rolling force is reduced at least in a last stand and the rolling force is increased in stands upstream of the last stand. 
     
     
       15. The method according to claim 1, comprising analyzing processes occurring during cooling of the strip on a run-out roller table and in a coil and simultaneously strip elongations or shortenings in a body portion as well as in strip edge portions, and compensating determined length changes by an appropriate presetting of the adjusting elements at least in the last stand. 
     
     
       16. The method according to claim 1, comprising using mechanically acting adjusting elements and non-mechanical adjusting elements including positive or negative thermal adjusting elements for supporting the mechanically acting adjusting elements. 
     
     
       17. The method according to claim 1, comprising comparing the measured surface unevenness shape with the intended evenness shape and utilizing the difference for adaptation purposes. 
     
     
       18. The method according to claim 1, comprising analyzing the difference between the determined surface unevenness shape and the intended evenness shape and dividing the difference into parabolic and portions of higher degree, and utilizing the adjusting elements accordingly in accordance with their effect.